U.S. Pat. No. 5,217,515, which issued to Geno Guglielmi on Jun. 8, 1993 and is entitled “Abatement of Tinkles in Wire Mesh” (hereinafter the Guglielmi patent, the contents of which are incorporated herein in their entirety by reference), sets forth a long-standing problem in the field of filters made from knitted wire mesh, namely, the presence of “tinkles” (also known as “gotchas”) in knitted wire mesh and thus in filters made from such mesh. The Guglielmi patent at column 1, lines 48-56, describes the source of tinkles as follows:                When knitted wire mesh is cut, it results in the production of loose pieces of scrap commonly known in the wire knitting industry as tinkles. The material making up the tinkles had formally been a portion of the knit. In other words, a tinkle is a knitted loop, or a portion of a knitted loop, which has been cut. Tinkles are of irregular shape and distribution and have no predetermined location, size or shape. However, they do tend to remain near the cut line where they were formed.        
FIGS. 1 and 2 hereto are copies of the corresponding figures of the Guglielmi patent which show a knitted wire mesh sock 10 and its associated tinkles 20 formed when the sock was cut from a continuous length of wire mesh (a continuous tube of wire mesh) produced by a circular knitting machine. As described in the Guglielmi patent at column 3, lines 36-39: “Tinkles are portions of cut knit loops. They do not have a characteristic size or shape. Indeed, the act of cutting the mesh can distort the wire to produce shapes not found in the original knit.” Having come from the knitted wire mesh, tinkles are composed of metal and are thus undesirable for most filter applications and impermissible for applications where the introduction of small pieces of metal into the gas or liquid stream being filtered cannot be tolerated, e.g., the filtering of the gases produced by an airbag inflator or the filtering of a fuel stream being provided to an internal combustion engine.
As described in the Guglielmi patent, efforts have been made to solve the tinkle problem by shaking the knitted wire mesh sock or picking the tinkles off by hand (Guglielmi patent at column 1, lines 59-61). These are highly labor-intensive processes and do not guarantee that filters made from the socks will be free of tinkles. As an alternative to trying to remove the tinkles, efforts have also been made to try to immobilize the tinkles. The Guglielmi patent represents one such effort in which electric resistance welding is used to bond tinkles to the wire mesh.
U.S. Pat. No. 5,849,054, which issued on Dec. 15, 1998 to Katsuhide Fujisawa and is entitled “Filter for an Inflator” (hereinafter the Fujisawa patent, the contents of which are incorporated herein in their entirety by reference), shows another immobilization approach in which, in making a filter, the sock is folded upon itself so that the cut ends of the sock end up buried inside the filter. FIG. 3 hereto is a copy of Fujisawa's FIG. 6(b′) which shows a folded sock in which knitted wire mesh 15 covers cut ends 14 of the mesh.
As the Guglielmi and Fujisawa patents illustrate, the mindset of inventors working on knitted wire mesh filters has been to accept tinkles as a fact of life and then look for ways of dealing with the tinkles. Unfortunately, no matter how sophisticated a tinkle control technique may be, at the end of the day, there can be no guarantee that every last tinkle has been dealt with. As indicated above, for a variety of applications, e.g., in-line fuel filters, airbag inflators, and the like, such uncertainty can be unacceptable. As discussed fully below, in accordance with the present disclosure, a completely new approach has been taken to the tinkle problem, namely, to make knitted wire mesh filters without generating a single tinkle. In this way, for the first time, knitted wire mesh filters that are guaranteed to be tinkle-free can be made.